1. Field of the Invention
This invention relates generally to the field of wells, particularly to the field of establishing branch wells from a parent hydrocarbon well. More particularly the invention relates to establishing multiple branch wells from a common depth point, called a node, deep in the well.
2. Description of the Related Art
Multiple wells have been drilled from a common location, particularly while drilling from an offshore platform where multiple wells must be drilled to cover the great expenses of offshore drilling. As illustrated in Figures 1A and 1B, such wells are drilled through a common conductor pipe, and each well includes surface casing liners, intermediate casing and parent casing as is well known in the field of offshore drilling of hydrocarbon wells. U.S. Pat. No. 5,458,199 describes apparatus and methods for drilling multiple wells from a common wellbore at or near the surface of the earth. U.S. Pat. No. 4,573,541 describes a downhole take-off assembly for a parent well which includes multiple take-off tubes which communicate with branched wells from a common point.
Branch wells are also known in the art of well drilling which branch from multiple points in the parent well as illustrated in FIG. 2. Branch wells are created from the parent well, but necessarily the parent well extends below the branching point of the primary well. As a result, the branching well is typically of a smaller diameter than that of the primary well which extends below the branching point. Furthermore, difficult sealing problems have faced the art for establishing communication between the branch well and the primary well.
For example, U.S. Pat. No. 5,388,648 describes methods relating to well juncture sealing with various sets of embodiments to accomplish such sealing. The disclosure of the '648 patent proposes solutions to several serious sealing problems which are encountered when establishing branches in a well. Such sealing problems relate to the requirement of ensuring the connectivity of the branch casing liner with the parent casing and to maintaining hydraulic isolation of the juncture under differential pressure.
A fundamental problem exists in establishing branch wells at a depth in a primary well in that apparatus for establishing such branch wells must be run on parent casing which must fit within intermediate casing of the well. Accordingly, any such apparatus for establishing branch wells must have an outer diameter which is essentially no greater than that of the parent casing. Furthermore, it is desirable that when branch wells are established, they have as large a diameter as possible. Still further, it is desirable that such branch wells be lined with casing which may be established and sealed with the branching equipment with conventional casing hangers.
An important object of this invention is to provide an apparatus and method by which multiple branches connect to a primary well at a single depth in the well where the branch wells are controlled and sealed with respect to the primary well with conventional liner-to-casing connections.
Another important object of this invention is to provide a multiple outlet branching sub having an outer diameter such that it may be run in a well to a deployment location via primary casing.
Another object of this invention is to provide a multiple outlet branching sub in which multiple outlets are fabricated in a retracted state and are expanded while downhole at a branching deployment location to produce maximum branch well diameters rounded to provide conventional liner-to-casing connections.
Another object of this invention is to provide apparatus for downhole expansion of retracted outlet members in order to direct each outlet into an arcuate path outwardly from the axis of the primary well and to expand the outlets into an essentially round shape such that after a branch well is drilled through an outlet, conventional liner-to-casing connections can be made to such outlet members.